The present invention relates to systems for accurately locating mobile devices as they move through an area, and in particular to a system providing location-sensing by tracking the locations of standard indoor light fixtures.
Increased use of light emitting diodes (LEDs) to provide for the primary environmental lighting in buildings and the like (termed herein “ambient lighting”) has raised the possibility of using these lights as beacons to identify the location of a mobile device through triangulation or the like. With such a system, each LED light may transmit a unique code in its light output identifying the light and/or its location. LEDs are particularly suited to this application because they can switch on and off at a high rate of speed imperceptible to human eyes but suitable for communicating data. The IEEE 802.15.7 standard has established a basis for visible light communication protocols allowing communication of up to 96 megabits per second.
U.S. patent application Ser. No. 14/980,103 filed Dec. 28, 2015, assigned to the assignee of the present application and hereby incorporated by reference, describes a system using light communication signals of this type to identify the location of a mobile device.
Navigation using data communicated through LED ambient lighting can require substantial investment in building infrastructure both to upgrade current light fixtures to network-connectable LED light fixtures and to properly configure a network for providing navigation signals. These costs are significant obstacles to the development and deployment of such systems.
U.S. patent application Ser. No. 15/164,195 filed May 25, 2016, assigned to the assignee of the present application and hereby incorporated by reference, describes a system that does not require network-connected light fixtures and in fact can work with standard fluorescent lights. The system associates the lights with unique frequency signatures that can identify light fixtures for navigation. A camera, for example, of a type found in a standard cell phone, may be used to determine the angle and signature of multiple lights to provide for triangulation type location calculations.
A standard camera provides for a convenient mechanism for identifying the angular bearing of multiple light sources, but also has significant limitations in this application. The limited bandwidth of the camera can make it difficult to distinguish between the signatures of multiple sources and high-frequency signature features. In addition, the low dynamic range of the camera makes it difficult to detect and measure the signature of individual light sources on a high ceiling, for example, in a warehouse type retail environment.